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How about a mirror wall?

Great idea! This is fun and makes the dining room less formal.

No pix are loading of your space, but most people don't like to watch themselves masticate, so art is the better option. If you're looking for some reflectivity consider a blingy chandelier

You might consider some simple and well chosen botanical prints to serve as a counter for your ornately traditional dining suite. They would relate nicely to the motif in your area rug and provide some freshness.

I don't have good visual of what's beneath the ornate mirror, but my guess is that it's a sideboard and I think your instincts are right - some simplification would be good there. As well as some curated tablescaping.

The less Formal aspect would be the style of plates you collage...Using some plates and some mirrors, platters, round, oval square mirrors or dishes, might be an arrangement you need to lay out on the table first, to get it just right?Using photos with one thing in common, such as matt color, photos black and white, or frames of a similar shade such as all white or all silver? or all painted sage green? might be an idea? Have fun making a change!

Beautiful rug. Use the colors in it to look for art.

Wedding pictures, no matter how attractive the bride, don't belong in the dining room. Make a hall gallery.

Go with large art to balance the china cabinet and dining table.

How about a wall of lovely pictures. Perhaps something like this?